Heretofore, a method for producing a corresponding unsaturated carboxylic acid or unsaturated nitrile by subjecting propylene or isobutylene to a vapor-phase catalytic oxidation or a vapor-phase catalytic ammoxidation has well been known. However, in recent years, a method for producing a corresponding unsaturated carboxylic acid or unsaturated nitrile by subjecting propane or isobutane in place of propylene or isobutene to a vapor-phase catalytic oxidation or vapor-phase catalytic ammoxidation reaction has attracted people's attention, and various types of oxide catalysts have been proposed. For example, oxide catalysts containing Mo—V—Nb—(Sb/Te) are disclosed in Patent Documents 1 and 2.
Further, examples in which a further enhancement of a catalyst performance has been achieved by adding a rare earth element or the like to the catalyst containing Mo and V are disclosed in Patent Documents 1, and 3 to 6.
Namely, when the corresponding unsaturated carboxylic acid or unsaturated nitrile is produced by subjecting propane or isobutane to a vapor-phase catalytic oxidation or a vapor-phase catalytic ammoxidation, the catalyst in which a rare earth element or the like is added to the oxide catalyst containing Mo—V is effective and many studies have so far been conducted on such catalysts as described above.
When the oxide catalyst containing Mo—V which has been added with a component of the rare earth element or the like as disclosed in Patent Documents 1, 3, 5 and 6 is used in the vapor-phase catalytic oxidation or the vapor-phase catalytic ammoxidation reaction of propane or isobutane, a yield of an object is not yet sufficient. Particularly, a carried catalyst favorable for a fluidized bed reaction tends to reduce the yield of the object. As for a reason for insufficient reaction performance, as disclosed in Patent Document 6, it is known that an addition component such as the rare earth element causes a unfavorable interaction with other metallic components in a process of preparing a slurry.
For example, there is a teaching in Patent Documents 1, 3, 5 and 6 to the effect that, when waster-insoluble solids having a relatively large average particle diameter are used, the unfavorable interaction to be generated in the process property of the slurry is reduced, to thereby enhance the yield of the object. However, in the above-described Patent Documents, not only there is no description about a uniform dispersion property of the addition component to the catalyst component at all, but also, since the solid raw material in use is not soluble in water, at the time of producing an industrial catalyst, there is a risk of clogging a pipe. Further, when an excess amount of the rare earth element or the like is added, an oxide particle made of the addition component is exposed on a surface of the catalyst and, then, a decomposition reaction of the object is promoted, to thereby reduce the yield.
In Patent Document 4, an impregnation method in which a desired element in a state of liquid is added to a catalyst which has been calcined is described. However, on this occasion, there is a problem in that, since the addition component is distributed merely on a surface of a catalyst particle and a surface of a pore, not only uniformity inside the particle is inferior, but also since it becomes necessary to calcine the catalyst again after being subjected to an impregnation operation, the operation is considered to be complicated and, also, since other metallic components are eluted in an impregnation solution, there is a risk of deteriorating the reaction performance and the like.
On the other hand, in the industrial catalyst, it is important to maintain a reaction performance not only at an initial stage, but also after a long period of use. A method in which a deteriorated catalyst is taken out and a new catalyst is replenished is considered. However, there is a problem in that such procedures as described above are time-consuming, a continuous operation is hindered and, also, it is economically not advantageous. Further, another method in which the deteriorated catalyst is taken out and regenerated and, then, replenished is considered. However, there is a problem in that such regeneration as described above is time-consuming, requires a complicated apparatuses and is not sufficiently performed. For this account, a catalyst which is small in reduction of the yield is required. For example, in Patent Document 2, an example of a catalyst in which an Mo—V—Nb—Te catalyst is subjected to a vapor-phase catalytic ammoxidation reaction of propane for 1300 hours while nearly maintaining a yield of acrylonitrile all the way is disclosed. However, an evaluation on the reaction in the above Document is made on that for such a relatively short period of time as 1300 hours and does not fully satisfy a performance necessary for an industrial application. Further, in regard to the catalyst containing Mo—V which has been added with the rare earth element or the like, there is no description on a performance of a long-term reaction at all.    Patent Document 1: JP 9-157241 A    Patent Document 2: JP 11-169716 A    Patent Document 3: JP 6-228074 A    Patent Document 4: JP 10-28862 A    Patent Document 5: JP 2000-202293 A    Patent Document 6: JP 2002-301373 A